Abdominal aortic aneurysm (AAA) is among the fifteen leading causes of death in the United States and has a prevalence of ˜10% in individuals over 60 years of age [Moxon et al., Current Problems in Cardiology, 35:512-548 (2010)]. AAA is characterized by extensive and permanent remodeling of the aortic wall, which results in a weakened and dilated aorta that is prone to rupture [Daugherty et al., Curr. Atheroscler. Rep., 4:222-227 (2002); Wanhainen, Scand. J. Surg., 97:105-109 (2008)]. Chronic inflammation caused by excessive macrophage infiltration of the aortic wall plays a key role in the pathophysiology of the disease by causing degradation of the extracellular matrix (ECM) along with apoptosis of endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) [Daugherty et al., Curr. Atheroscler. Rep., 4:222-227 (2002); Daugherty et al., Arterioscler. Thromb. Vasc. Biol., 24:429-434 (2004)]. Several pharmacologic therapies including statins, β-blockers and antibiotics have all failed in large clinical trials to prevent AAA, and there are no currently approved non-surgical therapies to treat AAA [Baxter et al. Circulation, 117:1883-1889 (2008); Hurks et al., European Journal of Vascular and Endovascular Surgery, 39:569-576 (2010)].
The pathophysiology of AAA has been well-described by analysis of both diseased human aortas and animal models. Initially, there is infiltration of inflammatory cells into the aortic wall followed by destruction of the normal aortic wall architecture. Human and mouse histologic studies of AAA have demonstrated the presence of extensive inflammatory macrophages and lymphocytes as major cellular components of the diseased aneurysmal tissue [Parry et al., Journal of Vascular Surgery, 52:145-151 (2010)]. These infiltrating cells exacerbate tissue injury by releasing cytokines (IL-6, interleukin-6; TNF-α, tumor necrosis factor-α), chemokines (MCP-1, monocyte chemotactic protein-1; CXCL-10, C—X—C motif chemokine-10) and adhesion molecules (ICAM-1, intercellular adhesion molecule-1; VCAM-1, vascular cell adhesion molecule-1) [Hui-Yuen et al., J. Immunol., 176:6294-6301 (2006); Jones et al., Circulation, 103:2260-2265 (2001); Rush et al., BMC Genomics, 10:298 (2009); Tieu et al., J. Clin. Invest., 119: 3637-3651 (2009)]. Excessive infiltration of macrophages and apoptosis of ECs and VSMCs are the most potent stimulators for the formation and progression of AAA because of their contribution to the widespread matrix degradation. Increased activation of matrix metalloproteinases (MMPs) results in both the degradation of collagen and collagenous matrix by MMP3 and MMP13 and the dissolution of the elastin by MMP2 and MMP9 [Cho et al., Surgery, 147:258-267 (2010); Keeling et al., Vascular and Endovascular Surgery, 39:457-464 (2005)]. This enhanced degradation of structural proteins, together with a reduced capacity to synthesize new matrix proteins, likely acts in synergy to progressively weaken the aortic wall, predisposing it to rupture. Various animal models of AAA are known in the art [Trollope et al., Cardiovascular Pathology, 20:114-123 (2011)].
The Notch signaling pathway is important in a wide spectrum of developmental processes, including angiogenesis, cardiovascular development and smooth muscle differentiation, but recently it has been studied in the molecular pathogenesis of cancer, cardiovascular disease and a diverse array of inflammatory diseases [Garg et al., Nature, 437:270-274 (2005); Gridley, Development, 134:2709-2718 (2007); Monsalve et al., J. Immunol., 176:5362-5373 (2006); Talora et al., Biochimica et Biophysica Acta (BBA)—Molecular Basis of Disease, 1782:489-497 (2008)]. The signaling pathway comprises of a family of four mammalian Notch receptors (1-4) that interact with the Jagged and Delta family of ligands [Kopan et al., Cell, 17:216-233 (2009)]. Notch1 is the best-studied receptor, and mutations in NOTCH1 have been linked to bicuspid aortic valve, aortic valve calcification, and thoracic aortic aneurysm (TAA) [Garg et al., Nature, 437:270-274 (2005); McKellar et al., J. Thorac. Cardiovasc. Surg., 134:290-296 (2007)]. In the canonical signaling pathway, Notch1 is activated after receptor-ligand binding at the cell surface, which induces proteolytic cleavage by several proteases, including γ-secretase. This results in the release and translocation of the Notch1 intracellular domain (NICD) into the nucleus where NICD binds and functions as a transcriptional activator [Bray, Nat. Rev. Mol. Cell. Biol., 7:678-689 (2006)]. Mice lacking Notch1 suffer embryonic lethality with profound cardiac and vascular defects, whereas heterozygous deletion of Notch1 is associated with aortic valve calcification [Gridley, Development, 134:2709-2718 (2007); Nigam et al., Journal of Molecular and Cellular Cardiology, 47:828-834 (2009); Nus et al., Arteriosclerosis, Thrombosis, and Vascular Biology, 31:1580-1588 (2011)]. In addition to its role in cardiovascular disease, Notch1 signaling has been shown to play a critical role in the development and activation of lymphocytes and macrophages via the upregulation of MCP-1 and ICAM-1 expression [Monsalve et al., J. Immunol., 76:5362-5373 (2006)]. Notch1 has also been suggested to regulate the expression of a variety of key inflammatory genes including MCP-1, inducible nitric oxide synthase (iNOS), ICAM-1, and VCAM-1 [Wang et al., J. Cell Biochem., 109:726-736 (2010)]. Several reports have shown decreased nuclear factor-κB (NF-κB) activity at basal levels and in response to external stimuli in mice with reduced Notch1 levels [Osipo et al., Lab. Invest., 88:11-17 (2008)]. However, the role of Notch signaling in the development and progression of AAA has not been previously studied.
There thus remains a need in the art for pharmacological treatments for AAA.